Ceftazidime is a cephalosporin beta-lactam antibiotic with good activity against Pseudomonas sp., which is being used increasingly in veterinary medicine. Pseudomonas sp. are associated with a large number of deaths of captive and stranded cetaceans (Buck et al., 1988; Dunn, 1990) with Pseudomonas putrefaciens being one of the more common isolates from clinically sampled animals (Vedros et al., 1990).

At Ocean Park, in Hong Kong, Pseudomonas pseudomallei, an endemic organism, has caused seasonal fatal septicemias in captive marine mammals (Bossart and Dierauf, 1990). Clinical success with ceftazidime used to treat humans has been excellent (Mandell and Sande, 1990), however, the drug is potentially nephrotoxic, causing renal tubular necrosis when given at high doses in humans (Barza, 1978). Also, strains of bacteria resistant to ceftazidime frequently emerge during treatment, making proper dosage important (Mandell and Sande, 1990).

The studies reported here were undertaken as the first step toward obtaining precise kinetic data on ceftazidime in the bottle-nosed dolphin (Tursiops aduncas) to develop an appropriate effective and safe therapeutic dosage regimen for treatment of dolphins diagnosed with Pseudomonas pseudomallei infections. This paper reports the data from the single dose trials of the study.

Methods

Two dolphins (Tursiops aduncas) were used in the single dose study. They were long-term captive specimens managed in the Ocean Park, Hong Kong facilities, and were free of outward signs of clinical disease. One animal was used twice after a suitable interval. Blood samples were taken prior to administration of drug and at predefined intervals thereafter (10, 20, 30, 45, 60, 75, 90, 120, 137, 150, 345, 360, 375, and 600 minutes post administration).

Drug for the studies was provided by Glaxo of Hong Kong. A dose of 17.4 mg/kg was given intramuscularly at time 0 of each of the three trials. All blood samples were centrifuged to obtain serum which was allocated into 1 nL vials and frozen immediately. Samples were shipped on dry ice to the analytical laboratory in North Carolina, under permit # 26038 from the USDA. All serum samples were assayed using a sensitive liquid chromatographic method which has been described (Tyczkowska et al., 1992).

To establish appropriate potentially effective serum levels of the drug, MIC and MBC studies were conducted on 2 strains of Pseudomonas pseudomallei isolated from two Tursiops aduncas (MIC 1.56 ug/ml; MBC 1.56 ug/ml).

Pharmacological data was analyzed using a computer curve stripping algorithm (R Strip).

Results and Discussion

All control samples were under detection limits of 0.5 ug/ml indicating sufficient time had elapsed between experiments when one animal was used twice in the study. Spiking studies reported previously (Tyczkowska et al 1992) confirmed 92.9 +/- 5.5 and 91.1 +/- 5.7% recovery at spiking levels of 20 and 2 ug/ml respectively indicating the methods used were accurate and specific. No evidence of metabolic conversion of the drug was detected in these trials.

Peak serum levels were achieved at about 30 minutes post injection. Mean serum levels remained above MIC for approximately 8 hours. When mean values for each dm point (N=3) were fit to a two compartment model, there was a model selection criterion of greater than 3.5 and a correlation (r2) of 0.993. Kinetic data indicated a TI/2 absorption of just over 14 minutes and a Tl/2 elimination of approximately 67 minutes. The area under the serum concentration-tin-ie curve (AUC) was 8168.8 and the area under the first moment curve (AUMC) was 941680 giving a mean residence U= (RMT) of 115.3 minutes.

From these results we are proceeding to study the kinetics of a multidose intramuscular therapy regimen in healthy animals using a 12 hour dosing interval with a goal of maintaining serum levels above NUC in excess of 50% of the dosing interval.

References

1.  Barza, M. (1978) The nephrotoxicity of cephalosporins: and overview. J. Infec. Dis. 137:560-573.

2.  Bossart, G.D. and L.A. Dierauf (1990) Marine Mammal Clinical Laboratory Medicine In: Handbook of Marine Mammal Medicine: Health, Disease and Rehabilitation, (L. Dierauf Ed.) CRC Press, Boca Raton, Fl. Pp. 1-52.

3.  Buck, J.D.; P.M. Bubucis; and S. Spotte (1988) Microbiological characterization of three Atlantic Whiteside Dolphins (Lagenorhynchus acutus) from stranding through captivity with subsequent rehabilitation and release of one animal. Zoo Biology 7:133-138.

4.  Dunn, J.L. (1990) Bacterial and mycotic diseases of cetaceans and pinnipeds In:Handbook of Marine Mammal Medicine: Health, Disease and Rehabilitation, (L. Dierauf Ed.) CRC Press, Boca Raton, Fl. Pp. 73-87.

5.  Mandell,, G.L. and Sande, M.A. (1990) Antimicrobial Agents In: The Pharmnacological Basis of Therapeutics 8th Edition (A. Goodman Gillman; T. RaH; A. Nies; and P. Taylor, Eds) Pergamon Press, Elmsford, N.Y. Pp. 1065-1097.

6.  Tyczkowska, K.L., S.S. Seay, M.K. Stoskopf, and D.P. Aucoin. (in press, 1992) Determination of ceftazidime in dolphin serum by liquid chromatography with ultraviolet-visible detection and conf tion by themio-spray liquid chromatography-mass spectrometry Chromatography.

7.  Vedros, N.; D. Chow; T. Ng; A. Tsang; K. MacKnight (1990) The Microbial Flora of Captive Cetaceans, their environment and food source at Ocean Park during 1989. Proceedings of the Int. Assoc. Aquatic Animal Med. 21:134.